Amplitude filter circuit for television receivers



Nov. 2, 1937. K. SCHLESINGER 2,097,804

AMPLITUDE FILTER CIRCUIT FOR TELEVISION RECEIVERS 4 Original Filed Oct. 5, 1934 Patented Nov. 2, 1937 UNITED STATES AMPLITUDE FILTER CIRCUIT FOR TELE- VISION RECEIVERS Kurt Schlesinger, Berlin, Germany 10 Claims.

The subject matter of the present invention which is a divisional one of application 747,011, filed 5 October 1934, is an arrangement for the reception of high-quality image transmissions employing a detector valve in push-pull connection.

For the reception of image transmissions it has already been set forth by the applicant in the Patent No. 2,068,768, January 26, 1937, on a previous occasion that a detector in push-pull connection and with modified dimensioning of the grid circuits is very well capable of being employed. With the push-pull detector there is still twice the total of grid condenser and grid capacity to charge, and moreover there must also be accepted the disadvantage of a loss in potential owing to the very small grid condenser.

The present invention is an improvement of the arrangement according to the Patent No. 2,068,768, January 26, 1937, in that the carrier frequency modulated with the picture contents currents is directly connected in push-pull fashion to the grids of a double-grid detecting valve. Further features of the invention will be set forth in connection with the appended drawing, in which in Figs. 1 and 2 there are set forth two circuits, in which loss of potential is avoided and also the detrimental capacity of the grid circuit is still further reduced. In both circuits there is employed a detector tube l6 having two grids I! and IS with small capacity by leading the connections out laterally, which grids in accordance with the invention are not arranged over the common cathode l9 twisted one within the other, but are situated side by side exactly symmetrically to the common anode 20 over the same. In this manner the grid current to the particular positive electrode will be greater than in the case of twisted grids. The carrier frequency is introduced by the anode circuit coil '2! of the final high-frequency amplifier-tube 22 into the grid circuit coil 23. The latter is tuned with its mutual operating capacity and own self-induction to the highest side band frequency of the television image, and is also critically damped by means of parallel resistances 2e, 25. The common bias of both grids as compared with the cathode is 0 volts or weakly positive, and is adjusted through the medium of a leak resistance 26 and battery 21. As will be seen, the mutual capacity of the grid circuit to be charged is merely equal to the total of the two grid-cathode capacities, which together may be reduced to approximately 5 cm., plus the total earth capacity of the coil 23. The latter may be made very small by large spatial disposal of this coil from all earthed conductors and also by the use of very thin wire, which at the same time enables to determine the damping of the coil by its own resistance, and small spatial arrangement in the vicinity of the detector tube. The resistance 26 is determined after knowledge of the total capacity from the condition that the discharge period constant should be smaller than the highest television frequency and seldom attains values of more than 100,000 ohms.

For balancing the inputs to the two grids there may be employed the following:

1. A differential neutralizing condenser 28, 29 with part capacities of approximately 2 cm., the rotor of which may not only be connected with earth, as shown in Fig. 1, but also with the centre of the coil, its capacity then having no adverse effect,

2. An electrostatic screening means 30 for overcoming a capacitative unbalance between primary and secondary coil.

This screening means, however, should only havea low capacity against the grid coil itself. The screening means may also be arranged to be shifted, for example in the form of a short ring, and then takes the place of the differential condenser 28, 29.

3. There may be employed the connection according to Fig. 2, in which the self-capacities 3!, 32 between the two windings in conjunction with an axial shiftability of the two coils in relation to each other, enable balancing to be performed, the total capacitative load of the secondary circuit being very small.

I claim:

1. In a push-pull grid current detector arrangement for grid detection, more particularly in the case of a television signal band of large width, modulated on an ultra-short carrier frequency, an input circuit comprising a transformer and a twin-grid detector valve, the primary of said transformer being coupled to the output of a carrier frequency amplifier, the secondary of said transformer being galvanically coupled at its ends to the two grids of said valve and being tuned by its self-induction and by its natural inherent capacities to the highest side band frequency of the modulated carrier frequency band, said valve comprising at least an anode, a cathode, and said two control grids, said cathode being connected to earth, a grid leak resistance connected between a middle tapping point of said secondary and earth.

2. In a push-pull grid-current detector arrangement for grid detection, more particularly in the case of a television signal band of large width, modulated on an ultra-short carrier frequency, an input circuit comprising a transformer and a twin-grid detector valve, the primary of said transformer being coupled to the output of a carrier frequency amplifier, the secondary of said transformer being galvanically coupled at its ends to the two grids of said valve and be-' ing tuned by its self-induction and by its natural inherent capacities to the highest side band frequency of the modulated carrier frequency band, said valve comprising at least an anode, a cathode, and said two control grids, said cathode being connected to earth, a grid leak resistance connected between a middle tapping point of said secondary and earth, and two damping resistances each connected between the one end of said secondary and earth across the two halves of said secondary, said resistances being so dimensioned as to render said secondary aperiodic.

3. In a push-pull grid current detector arrangement for grid detection, more particularly in the case of a television signal band of large width, modulated on an ultra-short carrier frequency, an input circuit comprising a transformer and a twin-grid detector valve, the primary of said transformer being coupled to the output of a carrier frequency amplifier, the secondary of said transformer being galvanically coupled at its ends to the two grids of said valve and being tuned by its self-induction and by its natural inherent capacities to the highest side band frequency of the modulated carrier frequency band, said valve comprising at least an anode, a cathode, and said two control grids having lateral leads to the outside of said valve, whereby said control grids have a low capacity with respect to said earthed cathode, said cathode being connected to earth, a grid leak resistance connected between a middle tapping point of said secondary I'- and earth.

4. In a push-pull grid-current detector arrangement for grid detection, more particularly in the case of a television signal band of large width, modulated on an ultra-short carrier frequency, an input circuit comprising a transformor and a twin-grid detector valve, the primary of said transformer being coupled to the output of a carrier. frequency amplifier, the secondary of said transformer being galvanically coupled at its ends'to the two grids of said valve and being tuned by its self-induction and by its natural inherent capacities to the highest side band frequency of the modulated carrier frequency band, said valve comprising at least an anode, a cathode, and said two control grids having lateral leads to the outside of said valve, whereby said control grids have a low capacity with respect to said earthed cathode, said cathode being connected ,to earth, a grid leak resistance connected between a middle tapping point of said secondary and earth, said grids being arranged side by side exactly symmetrically to said common anode and said common cathode.

5. In a push-pull grid current detector arrangement for grid detection, more particularly in the case of a television signal band of large width, modulated on an ultra-short carrier frequency, an input circuit comprising a transformer and a twin-grid detector valve, the primary of said transformer being coupled to the output. of a carrier frequency amplifier, the secondary of said transformer being galvanically coupled at its ends to the two grids of said valve and being tuned by its self-induction and by its natural inherent capacities to the highest side band frequency of the modulated carrier frequency band, said valve comprising at least an anode, a cathode, and said two control grids, said cathode being connected to earth, a grid leak resistance and a D. C. grid bias source connected in series between a middle tapping point of said secondary and earth.

6.111 a push-pull grid current detector arrangement for grid detection, more particularly in the case of a television signal band of large width, modulated on an ultra-short carrier frequency, an input circuit comprising a transformer and a twin-grid detector valve, the primary of said transformer being coupled to the output of a carrier frequency amplifier, the secondary of said transformer being galvanically coupled at its ends to the two-grids of said valve and being tuned by its self-induction and by its natural inherent capacities to the highest side band frequency of the modulated carrier frequency band, said valve comprising at least an anode, a cathode, and said two control grids, said cathode being connected to earth, a grid leak resistance and an. C. grid bias source connected in series between a middle'tapping point of said secondary and earth, said resistance being so dimensioned as to obtain a discharge time constant of the grid circuit shorter than the maximum television frequency of said signal band.

'7. In a push-pull grid current detector arrangement for grid detection, more particularly in the case of a television signal band of large width, modulated on an ultra-short carrier frequency, an input circuit comprising a transformer and a twin-grid detector valve, the primary of said transformer being coupled to the output of a carrier frequency amplifier, the secondary of said transformer being galvanically coupled at its ends to the two grids of said valve and being tuned by its self-induction and by its natural inherent capacities to the highest side band frequency of the modulated carrier frequency band, said valve comprising at least an anode, a cathode, and said two control grids, said cathode being connected to earth, a grid leak resistance connected between a middle tappingpoint of said secondary and earth, an electrical screening means arranged between said primary and said secondary for reducing capacity between said primary and said secondary.

8. In a push-pull grid current detector arrangement for grid detection, more particularly in the case of a television signal band of large width, modulated on an ultra-short carrier frequency, an input circuit comprising a transformer and a twin-grid detector valve, the primary of said transformer being coupled to the output of a carrier frequency amplifier, the secondary of said transformer being galvanical ly coupled at its ends to the two grids of said valve and being tuned by its self-induction and by its natural inherent capacities to the highest side band frequency of the modulated carrier frequency band, said valve comprising at least an anode, a cathode, and said two control grids, said cathode being connected to earth, a grid leak resistance connected between a middle tapping point of said secondary and earth, an electrical screening means shiftably arranged between said primary and said secondary for reducing capacity between said primary and said secondary.

9. In a push-pull grid current detector arrangement for grid detection, more particularly in the case of a television signal band of large width, modulated on an ultra-short carrier frequency, an input circuit comprising a transformer and a twin-grid detector valve, the primary of said transformer being coupled to the output of a carrier frequency amplifier, the secondary of said transformer being galvanically coupled at its ends to the two grids of said valve and being tuned by its self induction and by its natural inherent capacities to the highest side band frequency of the modulated carrier frequency band, said valve comprising at least an anode, a cathode, and said two control grids, said cathode being connected to earth, a grid leak resistance connected between a middle tapping point of said secondary and earth, an electrical screening means arranged between said primary and said secondary, and a differential balancing condenser, the stators of which are connected to the ends of said secondary, and the rotor to said screening means.

10. In a push-pull grid current detector arrangement for grid detection, more particularly in the case of a television signal band of large Width, modulated on an ultra-short carrier frequency, an input circuit comprising a transformer and a twin-grid detector valve, the primary of said transformer being coupled to the output of a carrier frequency amplifier, the secondary of said transformer being galvanically coupled at its ends to the two grids of said valve' and being tuned by its self-induction and by its natural inherent capacitiesto the highest side band frequency of the modulatedlcarrier frequency band, said primary and said secondary coils being arranged to be shiftable in relation to each other in axial direction for enabling balancing of the self capacities between said two windings, said valve comprising at least an anode, a cathode, and said two control grids, said cathode being connected to earth, a grid leak resistance connected between a middle tapping point of said secondary and earth.

KURT SCHLESINGER. 

